Wingless fruit flies might be a good option. You can get them pretty much year round in just about any pet store with a reptile department. The cultures last forever at room temp, and generally come ready to feed.

Well, I want you to all to LOL: I was removing live blackworms from the fridge. They're in a plastic shoebox. When placing the box back in the fridge I bumped the door: 1/4 of the live worms went airborne & landed square in a (luckily sealed) fridge door compartment!!!! Now, every time I open the fridge door, I have a mass of wriggling worms in the compartment next to my mustard and ketchup!!!
I'll have to remove them sooner or later, but it IS conveniet to get to the worms! I can just imagine if someone were to come over and check in the fridge... unless they were a fish keeper, and then it would be logical and no surprise at all...

Oops forgot to comment on the red cherry shrimp they will not eat your fry. But once the bettas are large enough they may eat the rcs. I bought some rcs I cant seem to keep them alive out of 25 I only have 4 left :( I love watching the shrimp almoat as much as I love watching my fry!